Adeno-associated virus (AAV) is a small defective DNA virus which requires adenovirus (Ad) as a helper for productive infection. The genome is a linear single strand (MW 1.4 x 10 to the 6th power) which contains a single structural gene. We intend to study the molecular biology of AAV at several levels: 1) DNA replication. How many Ad functions are required for AAV DNA replication? Various Ad temperature sensitive mutants will be tested for the ability to help AAV DNA replication in Ad transformed cells which already provide one necessary function for AAV replication. Is the intact genome required for DNA replication? DNA with specific deletions will be assayed for replication. 2) Initiation and termination of transcription. Control regions on the DNA will be sequenced and these sequences compared to sequences at the ends of the mRNA. 3) Recombination. Do AAV and adenovirus undergo recombination during coinfection? We shall look for adenovirus DNA molecules containing AAV nucleotide sequences in the electron microscope. 4) AAV as a provirus. In latently infected cells AAV DNA is integrated into host DNA. We shall characterize the integration using restriction enzymes. 5) Inhibition of SV 40. AAV inhibits SV 40 replication. We shall try to determine the level of inhibition (i.e. SV 40 DNA synthesis, synthesis of structural proteins or virion assembly).